1. Field of the Invention
The present invention relates to an apparatus for preventing light from being reflected from an internal surface of a zoom lens system.
2. Description of Related Art
Usually, a zoom lens system has at least front and rear groups of lenses which can be independently moved along the optical axis direction of the system to effect zooming operation. For instance, the assignee of the present application has proposed a lens shutter type of camera having a zoom lens, in PCT/JP No. 87/00293, in which front and rear groups of lenses can be independently moved in the optical axis direction of the zoom lens.
In a known zoom lens system, as mentioned above, the distance (separation) of the outermost effective light which is transmitted through the lenses, from the optical axis, varies in accordance with the zooming operation. The distance is large, especially on the outgoing side of light from the rearmost lens. This will be explained below with reference to FIGS. 18 to 20.
As can be seen in FIG. 18, the effective light Re which is transmitted through a rear group of lens L (which will be referred to as a rear lens group hereinafter) is emitted from the portion of the lens far from the optical axis O, at the shortest focal length. To the contrary, at the longest focal length, the effective light Re transmitted through the rear lens group L is emitted from a portion of the lens closer to the optical axis O, as shown in FIG. 19.
The sizes of the rearmost lens and a lens frame thereof are such that these elements do not intercept the effective light Re at any focal length. Namely, the sizes of the rearmost lens and the lens frame are determined in view of the outermost effective light Re which is transmitted through the rearmost lens at the portion thereof farthest from the optical axis O in a predetermined zooming range. Accordingly, at the longest focal length, there exist harmful light Rh which does not contribute to the formation of an image, as shown in the FIG. 20. The harmful light Rh is reflected in lens barrel block of the camera and reaches a film plane, resulting in an adverse influence on the quality of an image.
The primary object of the present invention is, therefore, to eliminate the above-mentioned drawback by providing a simple apparatus for preventing such harmful light, which would be otherwise incident upon the film plane, from being reflected in the lens barrel block of a zoom lens system.